1. Field of the Invention
The present invention relates to a communication system and, more particularly, to an apparatus for estimating phase information using a matched filter in a communication system.
2. Background of the Related Art
Generally, communication systems exchange system information with one another prior to sending/receiving payload data. A signal exchanged by the communication system is referred to as a pilot signal. FIG. 1 illustrates a related art pilot signal having a preamble for synchronization acquisition and a preamble for phase extraction (estimation).
FIG. 2 is a block diagram of a phase estimator using a matched filter according to the related art. The phase estimator includes a matched filter 110 that outputs synchronization signals using received data (I/Q) and converted information. A phase estimator 130, having averagers 137 and 138, outputs phase information using the received data and code information generated from a code generator. A CPU 120 initializes the averagers.
The matched filter 110 only serves to estimate synchronization. The meaning of estimating the synchronization is to generate an accurate point of time (e.g., locked position) of received data and information (e.g., locked energy). The synchronization estimate is used to identify a value with the largest correlation value, which is obtained by a multiplier and an adder in the matched filter 110.
The code generator (not shown) generates a code (PN_I (Inphase PN Code), PN_Q (Quadrature PN Code)) according to a synchronization time estimated by the matched filter 110.
Each of multipliers 131 through 134 multiplies received I and Q data by the respective synchronized code (PN_I, PN_Q) and each of adders 135 and 136 adds its individual code and the received data.
The averagers (MA: moving averages) 137 and 138 obtain and output an average value of the output signals from adders 135 and 136 for a predetermined time. Each average value output is used as phase information (Cos θ, Sin θ).
In such a phase estimator 130, averagers 137 and 138 are used to obtain more accurate phase information. The CPU 120 clears the initial values of the averagers 137 and 138, after estimating the synchronization with the matched filter, so that the averagers 137 and 138 cannot be affected by inaccurate data prior to estimating synchronization. That is, after clearing the initial values of the averagers to “0,” with the CPU 120, the output values of adders 135 and 136 are averaged for a predetermined time and used as the phase information.
However, in the related art, it takes a considerable time for the averagers to obtain an accurate phase value. Especially in the case of transmitting packet data, it is necessary to estimate synchronization as soon as possible and to modulate data by obtaining an accurate phase value.
However, the preamble is continuously transmitted in the related art. This is because it is possible to output complete phase information only by receiving a predetermined sequence of bits at the averagers 137 and 138. The predetermined sequence of bits takes precedence over the transmission of data. Thus, the performance of the transmission is degraded.
As illustrated in FIG. 1, a preamble for synchronization acquisition, a preamble for phase extraction, and data are transmitted in the case of transmitting the packet data. The preamble for phase extraction of predetermined bits must be transmitted regardless of the preamble for synchronization acquisition. In other words, the preamble for phase extraction is transmitted even after transmitting the preamble for synchronization acquisition, thereby reducing the transmission rate of the full data in the related method.